A San Francisco Muni rider took a detour to the hospital Sunday morning, after a fellow passenger hit him in what police say was an unprovoked attack.

According to the San Francisco Police Department, a 66-year-old man was getting ready to hop off the bus at Third and Market Streets at 8:30 a.m. Sunday.

As the man started to exit the bus, he was "closely followed" by a man in his 50s, police say.

Suddenly and without warning, the second man struck the first in the back of the head with a bicycle lock, police say.

"The assault was random/unprovoked," according to SFPD.

The victim suffered a "laceration/hematoma to back of head," the SFPD says. He was transported to hospital for treatment of his injuries, which are considered non-life-threatening by police.

His attacker apparently fled, as police say that no arrests have been made in this case.